| Rank | Abbreviation | Meaning |
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| ***** | OFFLINE AIRLINE, OFFLINE CARRIER. | Any airline other than the one or ones that own and/or control a particular computerized reservation system.
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| **** | DUAL DESIGNATED CARRIER. | Air carrier that uses another airline's code in flight schedule displays. See also code sharing.
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| *** | TRUNK CARRIER. | A major airline carrier, as evidenced by its extensive system of routes.
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| * | REGIONAL CARRIER. | An airline that serves only one clearly defined area of a country.
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| * | ONLINE CARRIER. | An airline that can provide immediate access through a computerized reservation system.
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| * | COMMON CARRIER. | Any company engaged in the transport of people or goods for profit.
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| * | CO-HOST CARRIER. | An airline that pays another to display its flights on a GDS.
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| * | FLAG CARRIER. | Strictly speaking, an airline that is run or owned (in full or part) by the country in which it is based. More loosely, any airline from a particular country. For example, “Continental and United ar
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| * | SHARED CODE CARRIER. | An airline that is listed on a GDS under the code of another airline.
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| * | CARRIER. | Any company that transports passengers or freight.
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| * | LOW-COST CARRIER. | An airline category defined primarily by low fares but also by a focus on reducing operating costs.
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